This lecture discusses air masses and fronts, including their defining characteristics. An air mass is a large body of air with similar properties that modifies the areas it moves over and is modified in turn. Air masses are classified by their moisture content (continental dry or maritime humid) and temperature source region (polar, tropical, arctic, or equatorial). Fronts occur at the boundaries between differing air masses, and the main types of fronts are cold, warm, stationary, and occluded fronts, which are distinguished by the movement and interaction of warm and cold air masses.

1. Lecture 26
Air Masses and Fronts

2.  Definition:
◦ Large (diameter > 1600
km) body of air
◦ Similar characteristics
throughout
◦ Recognizable entity; travel
as one
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Figure 7-2

3. ◦ Modifies area over which it moves
◦ Is changed by area over which it moves

4.  MOISTURE CONTENT
 c—continental, dry
 m—maritime, humid
 Temperature
 P—polar source region
 T—tropical source region
 A—arctic source region
 E—equatorial source region
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5. 5
Figure 7-1

6.  Southwestern Deserts – cT
 More moderate conditions in NW vs NE
– mP vs. cP

8. 8

9.  ―Front‖ of an air mass
 Midlatitude clashes
 Types of Fronts:
◦ Cold front: cold air advancing
◦ Warm front: warm air advancing
◦ Stationary front: no advance of air masses
◦ Occluded front: cold front overtakes warm front
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10.  Cold Front
◦ Fast moving, Steep frontal interface, warm air rises at
front
◦ Tall clouds, severe weather, ―Squall line‖
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11.  Warm Front
◦ Gentle slope of warm air rising above cool air
◦ Slow moving
◦ Sequence of clouds precedes front
◦ Steady precipitation
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12.  Stalled warm and
cold fronts
 Can produce
prolonged rain

13. Cold front
overtakes
warm front